Bush bearing and rack-and-pinion type steering apparatus for automobile using the same

Abstract

A bush bearing 7 includes a synthetic resin-made bush 17 having a circumferential groove 16 on an outer peripheral surface 15 thereof; an endless annular elastic member 18 fitted in the circumferential groove 16 of the bush 17 ; and a positioning means 19 for determining the position of the bush 17 in a B direction with respect to an inner peripheral surface 12 of a gear housing 6.

The invention claimed is: 
     
       1. A bush bearing for allowing a rack shaft having rack teeth meshing with teeth of a pinion to be supported movably in an axial direction of the rack shaft, comprising: a synthetic resin-made bush having at least one circumferential groove in an outer peripheral surface thereof; and an endless annular elastic member which is fitted in the circumferential groove of said bush,
 wherein said bush has an inner peripheral surface defining a through hole for the insertion and fitting therein of the rack shaft; at least one slit which partially severs the inner peripheral surface in a circumferential direction; a first contact portion which is formed on the inner peripheral surface for slidably coming into contact with an outer peripheral surface of said rack shaft on a line extending in a direction perpendicular to the axial direction of said rack shaft and an axial direction of the pinion; a second contact portion which is formed on the inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft; and a third contact portion which is formed on the inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, 
 wherein the second and third contact portions are arranged with an interval with respect to the first contact portion in the circumferential direction with the first contact portion interposed therebetween in the circumferential direction, 
 the second and third contact portions are arranged bilaterally symmetrically about the line, 
 the second and third contact portions are each arranged at an equiangular interval with respect to the first contact portion in the circumferential direction, 
 the first contact portion has a first inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, the second contact portion has a second inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, and the third contact portion has a third inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, 
 the inner peripheral surface of said bush has a first outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a first gap with respect to the outer peripheral surface of said rack shaft between the first and second contact portions, a second outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a second gap with respect to the outer peripheral surface of said rack shaft between the first and third contact portions, and a third outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a third gap with respect to the outer peripheral surface of said rack shaft between the second and third contact portions, 
 wherein the first inside inner peripheral surface at a portion thereof is adapted to slidably come into linear contact with a first outer peripheral surface of said rack shaft on an opposite side to the rack teeth side, excluding a second outer peripheral surface of said rack shaft on the rack teeth side, in the outer peripheral surface of the rack shaft, 
 the second inside inner peripheral surface at a portion thereof is adapted to slidably come into linear contact with a third outer peripheral surface on one side of the line, excluding the first and second outer peripheral surfaces of the rack shaft, in the outer peripheral surface of the rack shaft, 
 the third inside inner peripheral surface at a portion thereof is adapted to slidably come into linear contact with a fourth outer peripheral surface on the other side of the line, excluding the first, second and third outer peripheral surfaces of the rack shaft, in the outer peripheral surface of the rack shaft, 
 each of the first, second and third inside inner peripheral surfaces has a flat surface shape, and 
 an angle at which a first perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward a center of where said rack shaft would be positioned, in use from both edges in the circumferential direction of the first inside inner peripheral surface and by a side connecting the both edges and a second perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward the center of where said rack shaft would be positioned, in use, from both edges in the circumferential direction of the second inside inner peripheral surface and by a side connecting the both edges intersect each other, is identical to an angle at which the first perpendicular line and a third perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward the center of where said rack shaft would be positioned, in use, from both edges in the circumferential direction of the third inside inner peripheral surface and by a side connecting the both edges intersect each other. 
 
     
     
       2. The bush bearing according to  claim 1 , wherein each of the first, second and third inside inner peripheral surfaces has a center angle θ 1  of not less than 5° and not more than 90° about a center of said rack shaft. 
     
     
       3. The bush bearing according to  claim 1 , wherein each of the first, second and third contact portions protrudes from the inner peripheral surface of said bush toward the center of said rack shaft. 
     
     
       4. The bush bearing according to  claim 1 , wherein the inner peripheral surface of said bush is constituted by three convex-shaped, concave-shaped, or flat-shaped surfaces which are continuous to each other, and the first to third contact portions are respectively formed on the three surfaces. 
     
     
       5. The bush bearing according to  claim 1 , wherein the at least one slit is open at one of one end face and another end face in the axial direction of said bush and extends in the axial direction from the one of the one end face and the other end face to a vicinity of another one of the one end face and the other end face in the axial direction of the said bush past the circumferential groove. 
     
     
       6. The bush bearing according to  claim 1 , wherein said bush has a main body portion including the inner peripheral surface, the first, second and third contact portions, the outer peripheral surface, and the circumferential groove, and a plurality of protrusions provided integrally on the outer peripheral surface of the main body portion and spaced apart from each other in the circumferential direction, and the plurality of protrusions are adapted to come into contact with an inner peripheral surface of a housing through which the rack shaft is passed through. 
     
     
       7. The bush bearing according to  claim 6 , further comprising: positioning means for determining a position of said bush in the circumferential direction with respect to the inner peripheral surface of the housing. 
     
     
       8. A rack-and-pinion type steering apparatus for an automobile comprising: a pinion; a rack shaft having rack teeth meshing with teeth of said pinion; a housing through which said rack shaft is passed through; and the bush bearing according to  claim 1  which is fitted in said housing and movably supports said rack shaft with respect to said housing. 
     
     
       9. A bush bearing for allowing a rack shaft having rack teeth meshing with teeth of a pinion to be supported movably in an axial direction of the rack shaft, comprising: a synthetic resin-made bush having at least one circumferential groove in an outer peripheral surface thereof; and an endless annular elastic member which is fitted in the circumferential groove of said bush,
 wherein said bush has an inner peripheral surface defining a through hole for the insertion and fitting therein of the rack shaft; at least one slit which partially severs the inner peripheral surface in a circumferential direction; a first contact portion which is formed on the inner peripheral surface for slidably coming into contact with an outer peripheral surface of said rack shaft on a line extending in a direction perpendicular to the axial direction of said rack shaft and an axial direction of the pinion; a second contact portion which is formed on the inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft; and a third contact portion which is formed on the inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, 
 the second and third contact portions are arranged bilaterally symmetrically about the line, 
 the second and third contact portions are each arranged at an equiangular interval with respect to the first contact portion in the circumferential direction, 
 the first contact portion has a first inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, the second contact portion has a second inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, and the third contact portion has a third inside inner peripheral surface for slidably coming into contact with the outer peripheral surface of said rack shaft, 
 the inner peripheral surface of said bush has a first outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a first gap with respect to the outer peripheral surface of said rack shaft between the first and second contact portions, a second outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a second gap with respect to the outer peripheral surface of said rack shaft between the first and third contact portions, and a third outside inner peripheral surface which is disposed outwardly of the first to third contact portions in a radial direction and for being arranged with a third gap with respect to the outer peripheral surface of said rack shaft between the second and third contact portions, and 
 an angle at which a first perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward a center of where said rack shaft would be positioned, in use from both edges in the circumferential direction of the first inside inner peripheral surface and by a side connecting the both edges and a second perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward the center of where said rack shaft would be positioned, in use, from both edges in the circumferential direction of the second inside inner peripheral surface and by a side connecting the both edges intersect each other, is identical to an angle at which the first perpendicular line and a third perpendicular line in an isosceles triangle formed by two sides respectively extending in the radial direction toward the center of where said rack shaft would be positioned, in use, from both edges in the circumferential direction of the third inside inner peripheral surface and by a side connecting the both edges intersect each other.